Alkylbiphenyl compounds are known in the art for use as plasticizers (U.S. Pat. No. 2,172,391 and U.S. Pat. No. 2,115,524). Polycyclohexylbiphenyls containing at least three cyclohexyl groups are disclosed as plasticizing agents in U.S. Pat. No. 2,263,448. Partially hydrogenated polyphenyls are disclosed as plasticizers for vinyl polymers in U.S. Pat. No. 2,115,524 and U.S. Pat. No. 2,925,398. Partial hydrogenation (generally, at least about 20%) of a polyphenyl, such as terphenyl, results in a mixture comprised of monocyclohexylbiphenyl, dicyclohexylbiphenyl, and other terphenyl derivatives. Such mixtures are used commercially as PVC plasticizers.
One of the problems associated with all plasticizing materials is that of compatibility with the substrate into which it is milled. It is extremely important that the plasticizers remain in the treated material and not bleed to the surface and evaporate on aging or otherwise be removed from a complete distribution throughout the plastic. It has now been found that by use of a highly specific dialkyl biphenyl as plasticizer, improved compatibility with polyvinylchloride resins is obtained, particularly when used as a secondary plasticizer.